From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 72993C43381 for ; Thu, 11 Feb 2021 07:14:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4DC8C64EAA for ; Thu, 11 Feb 2021 07:14:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229731AbhBKHOZ (ORCPT ); Thu, 11 Feb 2021 02:14:25 -0500 Received: from mail.kernel.org ([198.145.29.99]:55912 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229517AbhBKHOS (ORCPT ); Thu, 11 Feb 2021 02:14:18 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 9ABFC64E70; Thu, 11 Feb 2021 07:13:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1613027617; bh=mFb5e+mcFjieGwWXbuKlq9q0UpNNbyeAq1/dwdNreuY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=r612v7W+RCFxSqtS+kG65T2iZaVwzZel4btR0FeMO2RkiMdOJ50IMLVhWxhHEVjeq RWIWvUmaSjvpNuRiWAmSDAzQxhntPIcqMrjyseEOwkEKs8om6hanjiK/XvklN5gvM6 4IRSCxhZL6+efdSsP/rZVDzTJVVy90foUNPuGiwSGjLg9nOaHA3e8aP5tOIg2ASxIJ Sp6nUBHKEK6j6j934tjzENjbujdOFEbYvxhqtUewKvYJI0DUbn0exEQp0qLWLIqa56 Txi+Gq3TeUWe+Arxca2HZee6BKF625xZfgl8d82Twk0iYyM/fBr2k70XriEGyOWcL0 DaEcHGkrjBISA== Date: Thu, 11 Feb 2021 09:13:19 +0200 From: Mike Rapoport To: Michal Hocko Cc: Mike Rapoport , Andrew Morton , Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , David Hildenbrand , Elena Reshetova , "H. Peter Anvin" , Ingo Molnar , James Bottomley , "Kirill A. Shutemov" , Matthew Wilcox , Mark Rutland , Michael Kerrisk , Palmer Dabbelt , Paul Walmsley , Peter Zijlstra , Rick Edgecombe , Roman Gushchin , Shakeel Butt , Shuah Khan , Thomas Gleixner , Tycho Andersen , Will Deacon , linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org, x86@kernel.org, Hagen Paul Pfeifer , Palmer Dabbelt Subject: Re: [PATCH v17 07/10] mm: introduce memfd_secret system call to create "secret" memory areas Message-ID: <20210211071319.GF242749@kernel.org> References: <20210208084920.2884-1-rppt@kernel.org> <20210208084920.2884-8-rppt@kernel.org> <20210208212605.GX242749@kernel.org> <20210209090938.GP299309@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 09, 2021 at 02:17:11PM +0100, Michal Hocko wrote: > On Tue 09-02-21 11:09:38, Mike Rapoport wrote: > > On Tue, Feb 09, 2021 at 09:47:08AM +0100, Michal Hocko wrote: > > > > > > OK, so IIUC this means that the model is to hand over memory from host > > > to guest. I thought the guest would be under control of its address > > > space and therefore it operates on the VMAs. This would benefit from > > > an additional and more specific clarification. > > > > How guest would operate on VMAs if the interface between host and guest is > > virtual hardware? > > I have to say that I am not really familiar with this area so my view > might be misleading or completely wrong. I thought that the HW address > ranges are mapped to the guest process and therefore have a VMA. There is a qemu process that currently has mappings of what guest sees as its physical memory, but qemu is a part of hypervisor, i.e. host. > > Citing my older email: > > > > I've hesitated whether to continue to use new flags to memfd_create() or to > > add a new system call and I've decided to use a new system call after I've > > started to look into man pages update. There would have been two completely > > independent descriptions and I think it would have been very confusing. > > Could you elaborate? Unmapping from the kernel address space can work > both for sealed or hugetlb memfds, no? Those features are completely > orthogonal AFAICS. With a dedicated syscall you will need to introduce > this functionality on top if that is required. Have you considered that? > I mean hugetlb pages are used to back guest memory very often. Is this > something that will be a secret memory usecase? > > Please be really specific when giving arguments to back a new syscall > decision. Isn't "syscalls have completely independent description" specific enough? We are talking about API here, not the implementation details whether secretmem supports large pages or not. The purpose of memfd_create() is to create a file-like access to memory. The purpose of memfd_secret() is to create a way to access memory hidden from the kernel. I don't think overloading memfd_create() with the secretmem flags because they happen to return a file descriptor will be better for users, but rather will be more confusing. -- Sincerely yours, Mike.